The inserts on Futura are the same standardised spacing as used on most boards, which of course (ultimately) have to be a researched average of all foot widths, with and without booties. Booties alone (even thin ones) can easily add 5mm each side in width to a standard foot - and that alone can throw the "ideal" spacing out by 10mm overall.
Add to that the extra "grip" that the upper section of many booties provides on the inside of the strap cover (mostly neoprene) and you definitely got a recipe for more strap exit stiction than normal..
Further, the new 2008 Slickstraps are pretty padded and soft (tends to be a more "grippy" mix than thinner harder straps, plus when they are brand new this further accentuates the difficulty of entry/exit (c/w nicely broken in after a few good sessions).
Strange enough, the K9 antitwist can actually (in select circumstances) work almost too well, and "lock" the strap twist/angle/curvature into a showroom position, which is not always the ideal entry/exit/control/comfort "twist angle".
(BTW the use of the K9 is recommended especially in the case of tight foot/bootie fit, as the extra space (height) resulting from the thickness of the K9 washer increases the stack height at each side of the strap before it starts it's radius curve over the foot.)
Fishscale deckpads also have more grip (resistance) to exit than entry (to avoid "falling out" in normal use ) - again with soft (new rubber) sole booties this can combine to semi velcro performance, less so as the pads loose their razor cut slits with some age, and further if the sole of the boot is older and harder rubber.
All small variables, but add them up and you can see the result.
As you're permanently on booties, the use of the lightweight Race Strap (or similar) will certainly "add" back more width insid ethe strap, as this is a thinner and less padded version. Normally, in freeride that is a less desireable comfort/control option (with bare feet) due to the reduced padding (less comfort) and the less precise screw hole adjustment (less control in critical situations) but (and here's the saviour !)- the use of booties actually resolves both of these issues in most cases very nicely.
Cheers ~ Ian